Field of the Invention
This invention relates to color cathode ray picture tubes, and is addressed specifically to an improved electrode assembly for an electron gun for such tubes. This invention has applicability to electron guns of many types and constructions, but is believed to be most advantageously applicable to three-beam unitized guns for color television cathode ray tubes.
In the unitized electron gun, common structures are used for gun parts, resulting in economies in manufacture and simplification of structure. The gun generates three electron beams by cathodic thermionic emission. The resulting beams are formed and spaced by a tandem succession of electrodes spaced along the central axis of the gun. The electrodes cause the beams to be focused on multiple phosphor groups located on the faceplate of the tube that contains the gun.
The three electron beams of an in-line gun lie side-by-side in the same plane. The inner beam, which normally activates the green-light-emitting phosphor deposits, proceeds on a straight line path down the center axis of the gun and through the gun toward its landing point on the phosphor-bearing faceplate of the cathode ray tube. The two outer beams, which activate the red-light-emitting and blue-light-emitting deposits, travel through the electrodes in paths generally parallel to the inner beam, then are diverted near the end of the gun to provide convergence of the three beams on the faceplate.
Recent developments in cathode ray tube design have led to an electron gun that employs an "open" main lens that provides the benefits of a reduction in spherical aberration and size of the beam "spots" that fall on the screen. A gun of this type is termed the COTY (combined optimum tube and yoke) gun. It utilizes a bipotential main focus lens comprising a pair of complementary electrodes each having a respective, common lens in adjacent, facing relationship.
The first component of the main focus lens, referred to as G3 in the succession of electrodes in the gun, has the form of an elongated "racetrack" shaped aperture. The second component, known as G4, or the anode electrode, has a beam-passing aperture in the form of a "dog-bone," which comprises a single aperture slightly enlarged at both ends through which the three electron beams travel.
The G4 electrode in a prior COTY gun is formed in three sections consisting first of a cup-shaped element that faces G3, and which has a dog-bone aperture. There is a second element, also cup-shaped, with the openings of the two cups in facing relationship. An apertured, plate-like electrode is sandwiched between the two electrodes; this electrode functions as a "carrier" in that it has extending claws that are embedded in the two opposed glass beads, or multiforms, that hold all the gun electrodes in permanent, fixed alignment and spacing. The convergence cup of the COTY gun is fastened to the bottom, or closed section, of the second cup-like second electrode.
Problems inherent in the G4 assembly of the COTY gun, which are obviated by the present invention, include difficulty in aligning the apertures of the three electrodes and welding the electrodes together, attaining proper spacing and planarity of opposing faces, and difficulty in attaching the convergence cup to the second electrode.